ceph: eliminate the recursion when rebuilding the snap context

Use a list instead of recursion to avoid possible stack overflow.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 5fd79ae..66a1a92 100644 (file)
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -127,6 +127,7 @@ static struct ceph_snap_realm *ceph_create_snap_realm(
        INIT_LIST_HEAD(&realm->child_item);
        INIT_LIST_HEAD(&realm->empty_item);
        INIT_LIST_HEAD(&realm->dirty_item);
+       INIT_LIST_HEAD(&realm->rebuild_item);
        INIT_LIST_HEAD(&realm->inodes_with_caps);
        spin_lock_init(&realm->inodes_with_caps_lock);
        __insert_snap_realm(&mdsc->snap_realms, realm);
@@ -320,7 +321,8 @@ static int cmpu64_rev(const void *a, const void *b)
  * build the snap context for a given realm.
  */
 static int build_snap_context(struct ceph_snap_realm *realm,
-                             struct list_head* dirty_realms)
+                             struct list_head *realm_queue,
+                             struct list_head *dirty_realms)
 {
        struct ceph_snap_realm *parent = realm->parent;
        struct ceph_snap_context *snapc;
@@ -334,9 +336,9 @@ static int build_snap_context(struct ceph_snap_realm *realm,
         */
        if (parent) {
                if (!parent->cached_context) {
-                       err = build_snap_context(parent, dirty_realms);
-                       if (err)
-                               goto fail;
+                       /* add to the queue head */
+                       list_add(&parent->rebuild_item, realm_queue);
+                       return 1;
                }
                num += parent->cached_context->num_snaps;
        }
@@ -420,13 +422,50 @@ fail:
 static void rebuild_snap_realms(struct ceph_snap_realm *realm,
                                struct list_head *dirty_realms)
 {
-       struct ceph_snap_realm *child;
+       LIST_HEAD(realm_queue);
+       int last = 0;
+       bool skip = false;
 
-       dout("rebuild_snap_realms %llx %p\n", realm->ino, realm);
-       build_snap_context(realm, dirty_realms);
+       list_add_tail(&realm->rebuild_item, &realm_queue);
 
-       list_for_each_entry(child, &realm->children, child_item)
-               rebuild_snap_realms(child, dirty_realms);
+       while (!list_empty(&realm_queue)) {
+               struct ceph_snap_realm *_realm, *child;
+
+               _realm = list_first_entry(&realm_queue,
+                                         struct ceph_snap_realm,
+                                         rebuild_item);
+
+               /*
+                * If the last building failed dues to memory
+                * issue, just empty the realm_queue and return
+                * to avoid infinite loop.
+                */
+               if (last < 0) {
+                       list_del_init(&_realm->rebuild_item);
+                       continue;
+               }
+
+               last = build_snap_context(_realm, &realm_queue, dirty_realms);
+               dout("rebuild_snap_realms %llx %p, %s\n", _realm->ino, _realm,
+                    last > 0 ? "is deferred" : !last ? "succeeded" : "failed");
+
+               /* is any child in the list ? */
+               list_for_each_entry(child, &_realm->children, child_item) {
+                       if (!list_empty(&child->rebuild_item)) {
+                               skip = true;
+                               break;
+                       }
+               }
+
+               if (!skip) {
+                       list_for_each_entry(child, &_realm->children, child_item)
+                               list_add_tail(&child->rebuild_item, &realm_queue);
+               }
+
+               /* last == 1 means need to build parent first */
+               if (last <= 0)
+                       list_del_init(&_realm->rebuild_item);
+       }
 }
 
 

diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index a2caa7b..ef9f32e 100644 (file)
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -883,6 +883,8 @@ struct ceph_snap_realm {
 
        struct list_head dirty_item;     /* if realm needs new context */
 
+       struct list_head rebuild_item;   /* rebuild snap realms _downward_ in hierarchy */
+
        /* the current set of snaps for this realm */
        struct ceph_snap_context *cached_context;